Infrared dispersion in SrTi${\mathrm{O}}_3$ at high temperature

Infrared reflection spectra of strontium titanate are reported as obtained with a scanning interferometer from room temperature up to 1200 K. A fit of the factorized form of the dielectric function to reflectivity data yields the temperature dependence of TO and LO frequencies, dampings, and TO oscillator strengths. The soft TO mode is found to be coupled with the next TO mode. A significant deviation of the soft-mode behavior from the Curie law is evidenced above 400 K. The temperature dependence of the soft-mode damping is discussed.